In an optical wavelength multiplexer transmission system, there are growing technologies in increasing bit rates of multiplexed optical signals and growing diversity of signal modulation. In order to support such increased bit rates and construct a more flexible network system, there is proposed a network system that incorporates a technology called “liquid crystal on silicon” (LCOS), which is capable of varying a transmission bandwidth of a wavelength. The LCOS technology is capable of varying a transmission bandwidth of a wavelength multiplexer-demultiplexer device based on a bit rate of an optical signal. Hence, a more flexible network system optimized for the bit rates and modulation systems may be proposed by incorporating the LCOS technology.
Meanwhile, in the wavelength division multiplexer (WDM) transmission, there is disclosed a technology of setting different values for bandwidths according to wavelength dependency of four-wave mixed light as the number of wavelengths consecutively allocated on wavelength grids and allocating a guard band to at least one wavelength grid between the consecutively allocated wavelength groups without allocating a signal light to the wavelength grid (e.g., Patent Document 1).
Further, in the WDM transmission utilizing a wavelength close to a zero dispersion wavelength lambda0 of an optical fiber, there is disclosed a technology of setting guard bands with predetermined power for reducing four light wave mixing including a zero dispersion wavelength lambda0 and allocating optical signals of plural channels to be multiplexed outside the guard bands (e.g., Patent Document 2).
Moreover, there is disclosed an optical switch to perform switching by selecting wavelengths of optical WDM signals. The optical switch includes a diffraction grating optical waveguide part and an optical switch processing unit for 2×2 unit to mutually switch between wavelengths (e.g., Patent Document 3).
In addition, there is disclosed a technology in which plural optical cross-connect devices are allocated based on outgoing path units. The optical cross-connect device includes a first WSS configured to output optical WDM input signals in N paths, a second WSS configured to store on an output side wavelength multiplexed signals received from the N paths and selectively outputs based on the wavelength received from the first WSS, a wavelength converting unit configured to convert the multiplexed signal received from the second WSS into a predetermined wavelength, and an AWG configured to multiplex W wavelengths input from the wavelength converting unit (e.g., Patent Document 4).